imx: spl: enable CONFIG_SPL_WATCHDOG_SUPPORT

This commit 4bdcbe60 removes reset_cpu
which breaks SPL build when DEBUG macro defined.

"
arch/arm/lib/built-in.o: In function `do_reset':
~/uboot/arch/arm/lib/reset.c:45: undefined reference to `reset_cpu'
scripts/Makefile.spl:244: recipe for target 'spl/u-boot-spl' failed
"
Enable CONFIG_SPL_WATCHDOG_SUPPORT to fix this issue.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Tim Harvey <tharvey@gateworks.com>
Acked-by: Eric Nelson <eric@nelint.com>

include/configs/imx6_spl.h

@@ -34,6 +34,7 @@
 #define CONFIG_SPL_SERIAL_SUPPORT
 #define CONFIG_SPL_I2C_SUPPORT
 #define CONFIG_SPL_GPIO_SUPPORT
+#define CONFIG_SPL_WATCHDOG_SUPPORT
 
 /* NAND support */
 #if defined(CONFIG_SPL_NAND_SUPPORT)